This application is based on Japanese Patent Application No. 2008-329301 filed with the Japan Patent Office on Dec. 25, 2008, the entire content of which is hereby incorporated by reference.
1. Technical Field
The present invention relates to a servo system and a safety control device suited for enhancing the safety of the servo system.
2. Related Art
A servo system is used in positioning control and the like of a movable part in various types of machines.
This type of servo system includes a servo system including a servo motor for driving various types of machineries, an encoder attached to the servo motor, a servo amplifier for controlling the operation of the servo motor, an upper level controller such as a programmable controller (PLC) for outputting position command information to the servo amplifier. The servo amplifier controls a drive current to the servo motor such that the position (angle) information from the encoder matches the position command information provided from the upper level controller.
For such a servo system, a waterwheel electric servo device, including a servo motor and a servo amplifier, for driving a guide vane of the waterwheel is disclosed in Japanese Patent No. 3525401. In such a servo device, an output voltage waveform of the servo amplifier is monitored, and an alarm is set off and a guide vane closing device for backup is activated, and the waterwheel is stopped when abnormality of the servo amplifier is detected.
However, Japanese Patent No. 3525401 relates to a drive device for the waterwheel and cannot be applied to various servo systems, and furthermore, it is insufficient with regards to safety function since the abnormality of the output voltage waveform of the servo amplifier is merely monitored.
A servo controller having a safety function for controlling to a safety side when failure occurs has also been proposed, but the entire system needs to be interchanged along with a dedicated servo amplifier, servo motor, and encoder when using such a servo controller.
If the entire servo system is interchanged, the cost becomes high and the know-how etc. accumulated in the existing servo system developed and customized by a user become a waste, and a new servo system needs to be rebuilt.